Mammalian Peptidylglycine α-Amidating Monooxygenase mRNA Expression Can Be Modulated by the La Autoantigen

Abstract

Peptidylglycine α-amidating monooxygenase (PAM; EC 1.14.17.3) catalyzes the COOH-terminal α-amidation of peptidylglycine substrates, yielding amidated products. We have previously reported a putative regulatory RNA binding protein (PAM mRNA-BP) that binds specifically to the 3′ untranslated region (UTR) of PAM-mRNA. Here, the PAM mRNA-BP was isolated and revealed to be La protein using affinity purification onto a 3′ UTR PAM RNA, followed by tandem mass spectrometry identification. We determined that the core binding sequence is approximately 15-nucleotides (nt) long and is located 471 nt downstream of the stop codon. Moreover, we identified the La autoantigen as a protein that specifically binds the 3′ UTR of PAM mRNA in vivo and in vitro. Furthermore, La protein overexpression caused a nuclear retention of PAM mRNAs and resulted in the down-regulation of endogenous PAM activity. Most interestingly, the nuclear retention of PAM mRNA is lost upon expressing the La proteins that lack a conserved nuclear retention element, suggesting a direct association between PAM mRNA and La protein in vivo. Reporter assays using a chimeric mRNA that combined luciferase and the 3′ UTR of PAM mRNA demonstrated a decrease of the reporter activity due to an increase in the nuclear localization of reporter mRNAs, while the deletion of the 15-nt La binding site led to their clear-cut cytoplasmic relocalization. The results suggest an important role for the La protein in the modulation of PAM expression, possibly by mechanisms that involve a nuclear retention and perhaps a processing of pre-PAM mRNA molecules.

ACKNOWLEDGMENTS

We are very to grateful to R. V. Intine and R. J. Maraia (Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD) for providing the GFP-hLaΔ316-322 construct. We thank Ger J. M. Pruijn (University of Nijmegen, Nijmengen, The Netherlands) for generously providing monoclonal antibody SW5 to the La antigen. We thank S. Schwartz (Uppsala University, Uppsala, Sweden) for generously providing the pTrc-His-La vector. We also thank P. M. Martin (Laboratoire de Transfert d'oncologie biologique, AP-HM) for his encouragement during the completion of these studies. We thank Véronique Gagna for her excellent secretarial assistance.

This work was supported by institutional funds of the CNRS and Inserm as well as by the Danish Biotechnology Instrument Centre (DABIC). F.B. was financed by the Association pour la recherche contre le cancer (ARC). J.B. was financed by Biacore AB (Uppsala, Sweden).